Most reinfections are initiated within tissues that comprise a frontline barrier with the outside world, such as the gastrointestinal, respiratory, and genitourinary mucosae. Memory CD8 T cells protect against intracellular pathogens by scanning host cell surfaces, so their migration patterns directly impact their ability to detect reinfection. It was recently discovered that a major lineage of memory CD8 T cells, termed resident memory (TRM), occupies mucosal tissues without recirculating. However, TRM act as first responders against reinfection events that are initiated in barrier tissues, and they greatly accelerate pathogen control and decrease disease. Thus, eliciting TRM may be an important goal for T cell vaccines against mucosal pathogens. Because TRM are not present within the easily sampled peripheral blood, and also because they were previously conflated with recirculating effector memory T cells, TRM have not yet been well characterized. This proposal will address major gaps in our current understanding of TRM. The hypothesis that TRM comprise different subsets, but share lineage defining markers will be tested using model infections in mice, parabiotic surgeries, and transcriptional profiling. Defining and validating bona fide markers will allow othe investigators to examine TRM biology even in systems where monitoring recirculation is impractical, or impossible (e.g. in humans), and will put the field on a firmer molecular foundation. Preliminary data indicating that TRM regulation differs from conventional T cell memories will support investigations into TRM longevity, maintenance requirements, and issues of homeostatic regulation in nonlymphoid tissues; issues with immediate relevance for vaccination. While CD8 T cells are thought to comprise an entirely separate arm of the immune system from antibodies, provocative preliminary data supports the hypothesis that CD8+ TRM act as sensory cells within the mucosae that are capable of rapidly increasing mucosal antibody concentrations in the event of reinfection. This proposal will explore the underlying mechanisms for this novel observation, which may provide further rationale for coupling T cell vaccination approaches with conventional humoral vaccine approaches for protecting against intractable pathogens such as HIV. Lastly, this proposal will test novel hypotheses related to augmenting TRM establishment within desired mucosal sites using a strategy that could be feasibly translated to humans. Practicably achieving this goal is still one of the major ambitions in T cell vaccinology. In summary, significant expertise will be leveraged to pursue fundamental biology into the emerging field of T resident memory, with very high health relatedness and potential for impact. New discoveries made here regarding TRM regulation, defining markers, longevity, function, and permissiveness to manipulation could have wide ranging impact not only for vaccines, but other T cell mediated immunological processes in tissues, including immunopathology, tumor immunosurveillance, and autoimmunity.